1) Field of the Invention
The invention relates to a crosslinkable powder composition which is redispersible in water and also to its use.
2) Background Art
EP-A 601518 describes crosslinkable dispersion powders which are redispersible in water and based on carboxyl-containing acrylate copolymers which are dried in the presence of polyvinyl alcohol and can contain polyvalent metal ions for crosslinking. Similar crosslinkable dispersion powders are also known from U.S. Pat. No. 3,409,578 in which powder compositions comprising carboxyl-containing polymers and/or carboxyl-containing protective colloids are crosslinked in the presence of polyvalent metal ions A disadvantage is that such compositions comprising polyvalent metal salts often liberate acid in the presence of water and tend to crosslink prematurely, especially in contact with moisture.
To avoid premature crosslinking, EP-A 702059 (U.S. Pat. No. 5,608,011) proposes using crosslinkable dispersion powders comprising N-methylol-containing copolymers and a catalyst combination of water-soluble or water-dispersible peroxo acid salts or reducing agents. EP-B 687317 describes crosslinkable powders which are redispersible in water and are based on N-methylol-functional copolymers which crosslink on heating. A disadvantage of the latter powder is the fact that exclusively heat-crosslinkable powders cannot be used in many applications.
EP-A 723975 discloses crosslinkable dispersion powders based on copolymers containing epoxide groups. For crosslinking, external crosslinkers such as polyamines, polycarboxylic acids, hydroxy-functionalized polymers and polyvalent metal salts are added. A problem with the use of polyamines or polyvalent metal salts is the low storage stability. The use of polycarboxylic acid or hydroxy-functionalized polymers does not impair the storage stability; however, elevated temperatures have to be employed for the reaction with the epoxy groups since otherwise the stabilization, as indicated in the application, of the dispersion powders by customary protective colloids would not be possible.
EP-A 721004 discloses crosslinkable, redispersible powder mixtures which comprise film-forming polymer particles having at least one functional, crosslinkable group. The crosslinkable group can also be introduced via the protective colloids. For crosslinking, this document, too, recommends the addition of an external crosslinker comprising at least one reactive component which forms nonionic bonds with the functional groups after the mixture is redispersed in water.
It is an object of the invention to provide a crosslinkable polymer powder composition which is redispersible in water and has good storage stability and offers the opportunity of matching the crosslinking rate to the respective field of application. A further object of the invention 1s to make available crosslinkable dispersion powders which can be crosslinked without addition of external crosslinkers.